The invention relates to the field of electric arc welding and more particularly to a monitor for monitoring the parameters and/or internal control signals of an electric arc welder during a welding cycle for the purpose of determining quality related characteristics of each welding cycle. Further, the invention relates to the method of monitoring an electric arc welder during a welding cycle to provide information regarding the actual performance of the welder during each welding cycle.
For many years welding companies and welding engineers have been intent upon recording electrical characteristics of the operating parameters implemented by electric arc welders during various welding processes. Ziegenfuss 3,950,759 is representative of many monitors for electric arc welders. This patent is incorporated by reference as background information. Through the years, a variety of time monitors have been employed for electric arc welders to determine the time during which a welding is actually being performed. To this end, it is common practice to provide a timer, or program to measure the time of welding compared to the time the welder is idle. Shostek 3,359,561 is representative of several patents for measuring the time that an electric arc welder is operated during a set period, such as a work shift in a manufacturing plant. Consequently, it is common knowledge that during the arc welding cycle a timer, counter or similar time accumulation device can record the relative time between welding and non-welding. For illustrative purposes Shostek 3,359,561 is incorporated by reference.
With the advent of computers, microprocessors and other digital processing devices, such devices either external or internal of the electric arc welder, are employed for the purposes of measuring and documenting the operation of an electric arc welder. Again, several publications show the state of the art for computerized monitoring of an electric arc welder. To avoid the necessity for detailed explanation of the background associated with computerized monitors, Bloch 5,708,253 is incorporated by reference. In accordance with control technology as used in the field of electric arc welders, it is also common practice to employ a central microprocessor for controlling the inverter forming the power supply and other ancillary appliances of an electric arc welding installation, as illustrated in Bloch 5,708,253. When disclosing the software procedure employed in monitoring electric arc welders it is common practice to set forth the program implementation as a series of steps performed by the computer microprocessor or similar digital manipulation devices. A representative example of such standard technologies is disclosed in Bloch 5,708,253, which is incorporated by reference herein to avoid the necessity of explaining the state of the art.
All of these background patents are representative in nature and merely explain the state of the art in monitoring electric arc welders by using computer technology when manipulating an arc welder by computer software.
A more recent disclosure of a computer of CPU control circuit to monitor an electric arc welder is illustrated in Vaidya 6,051,805. This patent discloses a system for monitoring several parameters in an electric arc welder, such as current, wire feed speed and gas flow, while using a computer to manipulate the measured characteristics of the parameters to generate information regarding the operation of an electric arc welder. As background information, Vaidya 6,051,805 is also incorporated by reference as background information and the state of the art.
The present invention is implemented on a Power Wave electric arc welder manufactured and sold by The Lincoln Electric Company of Cleveland, Ohio. A patent disclosing characteristics of this electric arc welder is Blankenship 5,278,390 incorporated by reference as showing a representative electric arc welder of the type used in practicing the present invention. Such welder, as shown in FIGS. 11 and 13, includes a wave form or wave shape generator to generate the series of rapidly repeating wave shapes constituting a weld cycle with a cycle time. Such wave shape generator is used for a variety of welding processes, such as pulse welding. The concept is also employed for a surface tension transfer short circuit welding process of the type disclosed in Stava 6,051,810. The Stava patent is also incorporated by reference as background information showing the use of a wave shape generator for generating the individual wave shapes that are outputted by an electric arc welder to create a weld cycle during a weld time, which is a total time that the welder is operating for a single welding process.
These many patents incorporated by reference herein illustrate the state of the art to which the present invention is directed, which state of the art is well known by manufacturers of electric arc welders as well as welding engineers implementing welding processes by arc welders.
Manufacturers of electric arc welders have attempted to monitor operation of the welder to determine the quality of the weld and the efficiency of the welder during operation in a manufacturing facility. One of the latest attempts to monitor an electric arc welder is illustrated in Vaidya 6,051,805 where a computer or other programmed instrument is employed to monitor average current and the efficiency of the welding operation, which efficiency is expressed as the time welding is performed as a ratio of the total time of the work shift. In accordance with standard technology, this disclosed monitoring system includes a first control circuit which is in the form of a central processing unit with standard accessories such as RAM, EPROM, and CIA. A second control circuit is connected to the first circuit to input and output information during the monitoring procedure. The monitor gathers information over a period of time which is disclosed as extending over a few hours or up to 999 hours. The monitor determines welding efficiency and monitors time to determine average current and accumulated arc welding time for overall efficiency. In accordance with this patent, there is a capability of monitoring the current and wire feed speed, as well as gas flow during the welding procedure. All of this information is stored in appropriate memory devices for purposes of outputting to read the operating characteristics of the welder during the welding process. In this way, the productivity of the welder can be measured to calculate cost efficiency and other parameters. Monitoring of the electric arc welder, as suggested in this patent, has been attempted by other manufacturers to measure average current during a welding process. However, measuring average current, voltage wire feed speed or other parameters during a welding process and using this data for recording the performance of the welding operation has not been satisfactory. In the past, monitoring devices have no pre-knowledge of the parameters being monitored. They only have capability of monitoring that which is occurring, as opposed to comparing that which is occurring to a priori knowledge. Consequently, monitoring of parameters such as current voltage and even wire feed speed in the past, even using the advanced technology set forth in Vaidya 6,051,805, has been chaotic in response and incapable of determining the actual stability of the electric arc or whether the welding process is above or below desired parameter values. This information must be known for the purpose of rejecting a welding cycle and/or determining the quality of the weld performed during the welding cycle with desired accuracy. In summary, monitoring the operation of an electric arc welder when used for a variety of welding processes has not been satisfactory because there is no prior knowledge which can be used for the purposes of evaluating the welding process during its implementation. The high powered programming capabilities now available do not overcome the lack of a system for generating real time and accurate reading of the welder performance.
The present invention is directed toward a monitor and method of monitoring an electric arc welder as the welder performs a selected arc welding process that creates heretofore unobtainable information on the operation of the welder. Thus, use of standard, high power computer technology can be used on equally precise and intelligent data generated by the monitor. The inventive monitor and monitoring system employs known information during the welding cycle. The information is fixed and not varying. The monitor concentrates on specific aspects of the welding process to employ prior knowledge which is compared to actual performance. Thus, the stability and acceptable magnitudes or levels of a selected parameter is determined during a specific aspect of the welding process. The weld process is separated into fixed time segments with known desired parameters before monitoring. Then this data can be processed by any of the known computer techniques to evaluate aspects of the weld cycle.
In accordance with the invention the welding process is formed as a series of rapidly repeating wave shapes taken together to constitute the welding cycle with a cycle time. Each wave shape is created by a known wave shape generator used to control the operation of the electric arc welder. These wave shapes are divided into states, such as in a pulse welding process, a state of background current, ramp up, peak current, ramp down, and then back to background current. By dividing the known driving wave shape into states defined as time segments of the generated arc characteristics, any selected one of the states can be monitored by using the invention. Indeed, many states can be multiplexed. For instance, in the pulse welding process the state related to the peak current can be monitored. In accordance with the invention, that state of the welding process is monitored by being read at a high rate preferably exceeding 1.0 kHz. However, the invention is practiced at a reading rate as low as 100 Hz. Each of the actual welding parameters, such as current, voltage or even wire feed speed is detected many times during each peak current state of the wave shape used in the pulse welding process. In this manner, the ramp up, ramp down and even background current is ignored during the monitoring process of the individual state. Consequently, the peak current is compared with a known peak current. A function of the peak current can be used to detect variations in the actual peak current outputted from the electric arc welder. In the invention, a minimum level and a maximum level on the lower and higher side of the command peak current are used to determine the level of the peak current many times during each peak current state of the pulse weld wave shape. Whenever the current exceeds the maximum, or is less than the minimum, this event is counted during each wave shape. The total deviations or events are counted for a weld cycle. If this count is beyond a set number per wave shape or during the weld cycle, a warning may be given that this particular weld cycle experienced unwanted weld conditions. Indeed, if the count exceeds a maximum level the weld cycle is rejected. This same capability is used with a statistical standard deviation program to read the peak current many times during each peak current state of the wave shape to sense the magnitude of the standard deviation. In practice, the standard deviation is the RMS deviation calculation by the computer program. By using the present invention, the average peak current is calculated and recorded as well as the level conditions and the stability characteristics. In implementation of the present invention the root mean square of the current or voltage is also determined for each of the state being monitored, in the example the peak current state of a pulse wave shape. While the peak current level or standard elevation is monitored, the background current stage can be monitored by current level and duration.
The invention involves selecting a state in the wave shape and comparing the desired and known command signals for that state to the actual parameters of the welding process during that monitored state. The selection is based on a priori knowledge of waveform generator. For example, at specific WFSxe2x88x92WFS1, the waveform generator is programmed to adjust peak current to control arc length. The xe2x80x9cinformedxe2x80x9d monitor then select peak current segment as the monitored state, when welding at this specific WFS1. At another WFSxe2x88x92WFS2, however, the waveform generator is programmed to adjust background time to control arc length (and not peak current). The xe2x80x9cinformedxe2x80x9d monitor then select background time as monitored state and parameter, when welding at this new WFS. In contrast, a posteriori monitor has no idea that at different WFS, different aspect of waveform should be monitored to detect arc stability. Monitoring background time at WFS1, or monitoring peak current at WFS2 in this example, would be very ineffective. It is new to use a time segment of the wave shape for monitoring only this segment of the wave shape using prior knowledge of the desired values. This allows actual monitoring of the electric arc welding process and not merely an averaging over the total wave shape.
In accordance with the present invention, the monitor is characterized by the use of prior knowledge, as opposed to the normal process of merely reading the output parameters experienced during the welding process. Consequently, the monitoring greatly simplifies the task of detecting normal behavior of a welder when the normal behavior is a function of time and differs during only one aspect of the welding process. The invention is not as applicable to monitoring voltage in a constant voltage process, because the desired level of voltage is a known characteristic during the total weld cycle. However, in other welding processes when both the voltage and current vary during different segments of the wave shape, the present invention gives accurate readings of stability, RMS, standard deviation, average, below minimum and above maximum before the actual parameter being monitored during selected segments of the wave shape.
By using the invention, the time varying welding processes, such as pulse welding and short circuit welding, is monitored with precise accuracy and not by reading general output information. The monitor and system is activated at a selected time in each wave form which is the selected state or segment of the wave shape. The monitor compares actual parameters to the desired parameters in the form of command signals directed to the power supply of the welder. By using the present invention, monitoring can occur during only specific segments of the wave shape; however, in exceptional events, such as when the arc is extinguished or when there is a short circuit, a computerized subroutine is implemented by either voltage sensing or current sensing to restart the arc and/or correct the short. The subroutines for these events run parallel to the monitoring program. Consequently, these exceptions do not affect the overall operation of the monitor constructed in accordance with the present invention. These subroutines are constructed as exceptional states or time segments. The parameters or signals within these exceptional states are monitored in a similar fashion as disclosed above.
By using the present invention, production information over a calendar time, shift or even by operator can be accumulated for the purposes of evaluating the operation or efficiency of a welder. The monitoring of each weld cycle by monitoring a specific segment or state of the wave shape allows accumulation of undesired events experienced over time. This also allows a trend analysis so that the operator can take corrective actions before the welding process actually produces defective production welds. Trend analysis, defect analysis, accumulated defects, logging of all of these items and related real time monitoring of the electric arc welder allows direct intervention in a timely manner to take preventive actions as opposed to corrective actions.
The invention utilizes a wave shape generator allowing the wave shape to be divided into segments or states where the welding engineer knows the command signals for each of the specific segments. These command signals are created in accordance with the wave shape generator. An important aspect of the invention is the time segmentation of the welding signals or wave shapes into distinct states. This is a new concept for monitoring an electric arc welder. In the past, monitors were not set to known program behavior for a segment of the wave shape. Consequently, the present invention differs from prior art by employing time segmentation of the wave shape implemented to create a weld process. The wave shape for creating a weld process, is implemented from a generator that sets the constraints of each individual segment. These segments or states are monitored. Consequently, the inventive monitor is sensitive to the wave shape. The actual wave shape is processed but the monitor ignores certain aspects of the wave shape and monitors other aspects.
The present invention monitors a parameter during a certain time segment or state of the rapidly repeating pulses forming a total welding cycle. The monitoring is accomplished at a high rate such as over 1.0 kHz. In practice, for pulse welding the high rate of interrogation for monitoring is generally about 10 kHz. For short circuit welding, such as surface tension transfer, the interrogation rate is about 40 kHz. The current being monitored rapidly during the wave shape and the monitored voltage can be combined to produce a value representing watts, resistance and/or energy, when based upon time. The stability of these parameters can be determined by statistical standard deviation algorithm. By comparing the calculated parameter with a minimum/maximum level a level analysis is made. The novel monitoring concept is used to output the arc resistance, as well as the energy applied to the welding process during a specific segment or state of the many wave shapes constituting a total weld cycle. The ability to measure the resistance, watts, energy, voltage, and current over a specific portion of the wave shape during the actual welding process heretofore has not been possible. Such information is extremely important in quality control, maintenance and prediction of the characteristics of the welding process. By implementing rapid interrogation of a segment in the wave form, the instability of the parameter being monitored during that segment is determined by standard. deviation technology, such as an algorithm for RMS deviation. The welder alerts the operator and/or welding engineer when instability exist during a particular portion of the weld wave shape being performed. Instability is not weld quality, but it is a precursor of such quality allowing the operator and/or engineer to take corrective actions as the instability increases by the standard deviation readings during individual segments of the wave shape. Such instability is related to consistency. In turn, consistency of the weld process is related to weld quality and is predictive of the welding process being accomplished.
In accordance with the invention, the wave shape generator creates the wave shape being performed by the welder and the wave shape is segmented into states. During each state, the monitor reads the value of voltage and current many times at a rate exceeding 1 kHz. However, slower reading would still result in advantageous monitoring since a single segment is being monitored. The speed or rate of monitoring merely allows a more accurate depiction of momentary variations in the current or voltage. After measuring the current and voltage, the resistance, time variations and energy are available for comparison to a maximum and minimum level detector or for determining standard deviation. The level monitoring is related to the command signals for the time segment or state. Then determining stability by standard deviation, the command signal may be used as a datum or need not be used. Several segments are monitored during each welding cycle and are accumulated for the welding cycle to determine the overall weld characteristics and weld process performance of the cycle.
By using the present invention, the welder is commanded to create certain parameters at a certain level. The actual parameters are measured and compared to the threshold levels. Stability algorithms give a reading of stability. The output characteristics are generated for different states selected to be monitored. In the computer program different characteristics for the selected states are analyzed and outputted or stored. The invention uses commanded wave shapes for the purposes of segmenting the monitored data. The known commanded behavior is compared to the observed behavior for analysis by the monitor. Consequently, data segmentation of the wave shape reduces the chaotic output information heretofore obtained in monitors for electric arc welders. The data is obtained at a rate of at least about 1.0 kHz. In certain instances, as explained earlier, the data is collected at a rate of 10-40 kHz. Due to this rapid data acquisition rate, onboard processing of the data is preferred. Thus, the electric arc welder outputs hard copy or displaces on a screen the information processed by the monitor. The monitor uses a digital process device, such as a computer or microprocessor associated with the welder and having sufficient memory to store the information or to output statistical summaries of the information upon request. Such statistical summaries may be available rapidly or on an inquiry basis. By using prior knowledge and determining arc stability and performance, anticipated problems are avoided by correcting the welding process before defective welding is experienced.
The monitor of the present invention is also used to record wire feed speed during the welding cycle and control this speed. In addition, internal signals, such as the output of PID closed loop feedback controller, and the input to a pulse width modulator, are processed for statistical stability in a manner indicating the internal workings of the arc welder during the segmented monitoring. The monitor is used as a production monitor to register the time during welding for a time, such as a shift. The monitor is also used in a manner that does not generate rapid data measurement, but records time necessary for a state of the wave shape. In a short circuit welding process, the time during a short circuit is monitored to determine time variations during a welding cycle or from cycle to cycle. In a pulse weld process, the time during background current may vary at one wire feed speed. At another wire feed speed peak current may vary by design of the wave shape generator. Variations in these times are monitored by the present invention. Both the short and the background time are capable of being monitored because the wave shape is segmented. Thus, an important aspect of the invention is the segmentation of a known wave shape to develop data which is analyzed for the purposes of predicting and/or correcting the arc welding process. The background time variations in a pulse welding process is due to stick out changes and the time variations in short circuit welding is due to droplet size changes and weld pool movement. Thus, using the present invention statistical variations of time in background or time in short circuit provides information on arc stability that is monitored.
In summary, the invention monitors the operation of an electric arc welder by rapidly interrogating or reading the value of a welding parameter during a segmented state of the wave shape. The results of this rapid read, interrogation or xe2x80x9clookxe2x80x9d at the welding parameter are then stored for display externally or internally and, more importantly, are analyzed to monitor the welding process during a weld cycle and/or during a manufacturing shift. The analysis is by standard deviation such as a root mean square deviation for providing arc stability information. In practice xe2x80x9cstandard deviationxe2x80x9d is performed as the absolute deviation. In accordance with another aspect, the rapid reading during the wave shape state is analyzed from a level standpoint by comparison with a set level employed during the state. In the level determination, one aspect involves determining the number of times that the read or interrogated parameter value exceeds a preset maximum. In another aspect of the inverter, when the data read by the monitor is less than a preselected minimum the transition is recorded. By counting the number of transitions beyond the preselected minimum or maximum levels, the quality of the weld can be monitored either during the weld cycle or over a given period of time. In this manner, any drift of the welding parameter is detected in advance of an actual rejection.
The invention is used to monitor arc stability in weld development using synergistic and non-synergistic procedures. When a parameter is changed, the invention will determine if the change corrects stability or increases arc instability. By using the monitoring system of the invention, arc stability is determined as the welding process is changed or during the operation of a welding cycle. In this manner, the invention provides a diagnostic tool to analyze the wave shape by focusing on specific states making up the wave shape. The monitored parameters of the weld operation are current, voltage, global scale factor (GSF), time and their statistical characteristic. GSF is the output of a feedback closed loop controller used for arc length regulation, for example, a PID digital filter or error amplifier. Quantitative determination, specification and comparison of the arc quality and the various welding conditions is made possible by using the present invention. The invention provides information on the manner by which repeatable wave shapes are implemented during a total weld cycle.
The primary parameters monitored by the present invention are time, arc current, arc voltage and global scale factor. These parameters are analyzed for the purposes of stability over a total weld cycle on an average basis or on a stability basis. A minimum level and a maximum level monitoring is conducted by using the present invention. Although the total weld cycle of rapidly repeating wave shapes is monitored, the actual monitoring process is performed on a selected portion of each weld shape. By focusing on the individual states, in a total weld shape, variations during the selected state provide extremely high sensitivity and tremendously high level of real time knowledge and data.
The parameter being monitored is read many times during the state of a wave shape being monitored; however, the monitored state in practice should exceed 0.2-0.4 ms and the monitor rate or rate of reading data is generally greater than 10 kHz. By using the invention, the analyzed parameter during a selected state of the wave shape can be used to pass or reject a weld cycle. In accordance with an aspect of the invention, a warning signal is provided after a preselected number of deviations, but before a weld reject condition has been reached. Since arc stability is monitored during each state of the wave shape, the average stability of the entire weld is obtainable. Stability is read with a scale of 0-100, where 100 is the most stable arc.
Stability is calculated by an algorithm. In a pulse welding process as shown in FIGS. 2, 3, and 9A, the background current is monitored as a time segment of the wave shape. This segment is between t4 and t1. The mean background current {overscore (x)} is:       x    _    =            1      N        ⁢                  ∑                  j          =          1                N            ⁢              xe2x80x83            ⁢              x        j            
where N is the total count of background current states.
Standard deviation SD is:   SD  =                              ∑                      j            =            1                    N                ⁢                  xe2x80x83                ⁢                              (                                          x                j                            -                              x                _                                      )                    2                            N        -        1            
The unitless number known as the coefficient of variation CV is:   CV  =                    (        100        )            ⁢              (        SD        )                    x      _      
Stability=100xe2x88x92CV.
Consequently, the most stable background current is where the stability is 100. This same calculation is used for all segments being monitored.
In one aspect of the invention, absolute deviation is used as opposed to statistically standard deviation. The invention counts the times that a stability signal of a wave shape state is below the acceptable stability for welding. These transient counts are accumulated to determine whether the weld passes or fails. These analytical techniques employ the invention.
The invention is capable of performing several diverse procedures heretofore not obtainable with a high accuracy. For instance, running indication of absolute deviation of a parameter is provided. The invention also utilizes a running average indication that is updated while the welding data is being monitored. Maximum absolute deviation on a per weld basis is displayed for evaluation. Further, an indication of the average absolute deviation on a per weld basis is displayed. The new monitor logs the absolute deviations calculated for each weld. This information indicates arc stability. Other uses of the data obtained by the invention are within the skill of the art.
An object of the invention is the provision of a monitor capable of performing the functions herein stated.
In accordance with the invention, there is provided a device for monitoring an electric arc welder as it performs a selected arc welding process by creating actual welding parameters, such as arc current and arc voltage, between an advancing welding wire and a workpiece. The welding process is defined by a series of rapidly repeating wave shapes constituting a weld cycle with a cycle time. The wave shapes are segmented into states having command signals corresponding to the actual parameters to be processed during the time segment and a state time duration which may be fixed or variable. The monitor selects a specific state, reads one of the actual parameters periodically at a rate greater than 1 kHz and compares the actual parameter reading with a function or value of the command signal corresponding to the one of the actual parameters. This comparison generates an arc characteristic attributed to the selected state. The actual parameter during a state in the preferred embodiment, is analyzed stability as determined by the standard deviation. The parameter is also monitored for level deviations. After the stability has been determined by reading the standard deviation of the parameter during a particular state, the deviation of all states during a weld cycle are accumulated. This determines the total stability of the particular state being monitored.
In practical implementation of the invention, the stability from various signals are combined on a xe2x80x9ctime contributionxe2x80x9d method. In this method, the more accumulated time in state, the more weight is given to the signal. If multiple signals have the same state, the weights are equally distributed. This concept is illustrated in the following example.
In pulse welding, the peak time and background time are monitored for stability. Where tB is the background current time and tp is the peak current time:
The total background time TB is:       T    B    =            ∑              i        =        1            N        ⁢          xe2x80x83        ⁢          t      B      
The total peak time TP is:       T    p    =            ∑              i        =        1            N        ⁢          xe2x80x83        ⁢          t      p      
In the algorithm, stability of the peak current is:   100  -                              (                      CV                          t              B                                )                ⁢                  (                      T            B                    )                    +                        (                      CV                          t              P                                )                ⁢                  (                      T            P                    )                                    T        B            +              T        P            
In general:   Stability  =      100    -                            ∑                      i            =            1                    K                ⁢                  xe2x80x83                ⁢                              CV            i            *                    ⁢                      T            i                                                ∑                      i            =            1                    K                ⁢                  xe2x80x83                ⁢                  T          i                    
where i is the enumerator of the participating channel and K is the number of participating channels. If multiple channels share the same state, Ti will be equally distributed among these channels. For example, both background current (BC) and background time (BT) contribute to the stability, as follows:       Stability    =          100      -                                                                  CV                BC                            ⁡                              (                                                      T                    B                                    2                                )                                      +                                          CV                BT                            ⁡                              (                                                      T                    B                                    2                                )                                                                                        T                B                            2                        +                                          T                B                            2                                      ⁢                  xe2x80x83                ⁢        or                  Stability    =          100      -                                    CV            BC                    +                      CV            BT                          2            
The standard deviation of a state during a weld cycle indicates quality of the welding cycle. In accordance with another aspect of the invention, transition of the actual rapidly read parameter values with respect to a minimum or maximum level is detected and accumulated. The number or existence of transitions above the minimum or below the maximum level is indicative of the weld quality. By recording either stability of a parameter or level deviations of a parameter from weld cycle to weld cycle, the system of the invention detects trends in the welding operation allowing corrective action before actual defective welding is experienced.
In accordance with the present invention, a number of readings are performed during the selected time segment or state of each successive wave shape. In practice this rate is substantially greater than 1 kHz and is preferably about 10 kHz for pulse welding. In short circuit welding, it has been found that the preferred rate of reading parameters is in the neighborhood of 40 kHz.
In accordance with another aspect of the present invention, there is provided a monitor for an electric arc welder as it performs a selected arc welding process for creating actual weld parameters between an advancing welding wire and workpiece. The process is controlled by command signals to the power supply of the welder. This monitor is controlled by a wave shape generator for creating a series of rapidly repeating wave shapes constituting a weld cycle. The wave shapes each are segmented into time states. The monitor measures and records level deviations of the selected weld parameter during a selected one of the time states. The use of a wave shape generator for controlling the power supply allows division of the wave shape into states wherein level deviations of a parameter used in the welding is monitored. In accordance with another aspect of the present invention, the level deviation set forth in the inventive statement above is replaced by a statistical deviation measurement of a weld parameter. Standard deviation is recorded for a selected one of the states to determine stability of the welding operation.
Still a further aspect of the present invention is monitoring an electric arc welder as the welder performs a selected arc welding process by creating actual welding parameters between an advancing wire and a workpiece. The weld process is controlled by command signals to the power supply of the welder in the form of a series of rapidly repeating wave shapes divided into functional states. Level deviations of a selected weld parameter are detected at a selected rate during one of the selected states and the results are accumulated over the total weld time. In accordance with this aspect of the invention, stability of a selected weld parameter is monitored during one of the functional states for the total weld time. By either level detection or stability measurement, the operation of the welding process is monitored during each weld cycle or during a time shift period, such as a day or otherwise.
In accordance with another aspect of the present invention there is provided a method of monitoring an electric arc welder as the welder performs a selected arc welding process by creating an internal signal for controlling the power supply or the wire feed speed of the welding wire as it is advancing toward the workpiece. The internal signal, which can be the input to a pulse width modulator, is monitored to measure the stability of the internal signal during one of the states of the segmented wave shape. These internal signals of the arc welder are also interrogated at a rapid rate to generate an indication of stability by a standard deviation, or absolute deviation, of the internal signal during the selected time segment or state of the wave shape.
The primary object of the present invention is the provision of a monitor or monitoring method which utilizes the concept of generating wave shapes rapidly for controlling the power supply wherein the wave shapes are segmented into time states. The time states of successive wave shapes are monitored so the total wave shape is not monitored.
Yet another object of the present invention is the provision of a monitor and monitoring system, as defined above, which monitor and system repeatedly reads an output parameter, such as current or voltage during a segment of each wave shape to create a stability reading, such as a standard deviation, and a level reading relating to level transitions of the weld parameter at individual reading steps.
Another object of the present invention is the provision of a monitor and monitoring system, as defined above, which monitor and monitoring system is used to create a large number of output readings of a characteristic of the welding process where the weld characteristic is used during the welding process for measuring the performance, maintaining, and adjusting the electric arc welder.
Still another object of the present invention is the provision of a monitor and monitoring system for an electric arc welder, which monitor and monitoring system monitors precise portions of the wave shapes used to control the welder. Thus, the monitor accuracy is drastically increased since it contains substantial real time data based upon prior knowledge.
These and other objects and advantages will become apparent from the following description taken together with the accompanying drawings.